In a commercial process for the manufacture of adipic acid, cyclohexanol and cyclohexanone are oxidized with nitric acid in the presence of copper and vanadium catalysts. The resulting product contains adipic acid, as well as glutaric acid, and succinic acid. Conventionally, most of the adipic acid is removed from the product by crystallization, and the remaining portion of the product has in the past been treated in various processes to recover other useful products and the copper and vanadium catalyst metals. For example, in U.S. Pat. No. 4,375,552 to Kuceski the stream after crystallization and removal of most of the adipic acid is treated with an alcohol to form esters which are not soluble in the aqueous phase. The esters are then removed from the stream, and the catalyst metals, which remain in the aqueous phase, are recycled to the nitric acid oxidation step.
Ultrasonic agitation of various fluids during crystallization is known, for example, see U.S. Pat. No. 3,892,539 (1975) which shows fluidized bed crystallization with supersaturated fluidizing liquid--and ultrasonic frequency agitation which fractures larger crystals for seeds. In "Effect of Cavitation on the Kinetics of Crystallization from Solution" by Hofman, J. and Roubik, V. in Chem. Prum., 44(1), 18-19, 1994: The effect of ultrasound on the kinetics of crystallization of potassium sulfate from aqueous solutions was studied. The crystal growth rate was found to be enhanced by ultrasound for crystals up to a certain size (approx. 350 microns).
"Rapid Crystallization using Ultrasonic Irradiation--Sonocrystallization" by David R. Kelly et al. in Tetrahedron Letters, 34(16), 2689-90, 1993: Used ultrasonic irradiation to induce rapid crystallization of materials which normally only crystallize with difficulty.
"The Narrowing of Crystal Size Distributions in a Sonicator-MSMPR Crystallizer System" by Mydlarz, J. and Briedis, D. in Chem. Eng. Commun., 104, 291-305, 1991: Use of sonication was found to narrow the crystal size distribution.
"Shape of Crystals During Slow Crystallization" by Shopova, R. in God. Vissh. Khim.-Tekhnol. Inst., Sofia, Vol. Date 1979, 26(2), 68-74, 1980: Ultrasound was found to favor growth of one type of surface but not others.
"Effect of Ultrasound on the Latent Period of Crystallization from Spersaturated Solutions" by Kortnev, A. V. and Martynovskaya, N. V. in Sb., Mosk. Inst. Stali Splavov, 77, 98-100, 1974: Ultrasound was found to influence nucleation rate--increasing ultrasonic energy decreased induction period.